Bonjour!
Well, I am in a fairly similar situation, except that I am a tad older (just a tiny bit!) and spent 15 years in the US after working for a while in France. My wife and kids recently got their dual citizenship, and I am the "irreductible gaulois" - although more procrastinating than refusing to jump in.
Yes, I don't expect that the US/France agreement will disappear, but to be brutally honest, your few years of work in France are probably not worth very much. I know I am NOT betting on corresponding retirement money, just viewing it as optional tiny bit of icing on the cake. As to France possibly trying to tax me from overseas, well, they can try...
Tax-wise, I don't see much difference either way.
Pains me a bit to say so, but the potential for you to have an interesting career, to save solid money and to retire early and flexibly is much greater in the US. Also, if you want to have an experience in another country for a few years, the citizenship guarantees that you will be able to come back to the US if you wish to, which is not the case with a green card. An important backup option, if you ask me.
Overall, I'd advise that you take the plunge. No harm, and more flexibility down the road.
PS. as side note, I live pretty close to you (near Boston). If you want to come and chat 'live', feel free to contact me.